The alarming increase in smoking prevalence among young adults in recent years, and the disturbing development that 18-24 year-olds now have the highest smoking prevalence of any age group, argue for strong new theory-driven longitudinal investigations of smoking acquisition and cessation during young adulthood. Responding to this need, this study will capitalize on the exceptional characteristics of the Hutchinson Smoking Prevention Project (HSPP) cohort and a rare window of opportunity to (1) survey at ten years post high school the 8,291 surviving members of the HSPP cohort, and (2) conduct a staged series of scientific investigations to critically examine smoking acquisition, cessation, and relapse during the period of young adulthood. Using both existing and newly collected longitudinal data on the HSPP cohort, this study will (1) document changes in smoking behavior--smoking acquisition, smoking cessation, and relapse--throughout young adulthood, and use time-to-event analysis methods to investigate their prediction by significant young-adult life milestones, (2) investigate the roles of theoretically-based individual and environmental factors at the start of young adulthood, as well as in childhood and adolescence, in predicting changes in smoking-related behaviors during young adulthood, (3) investigate the roles of theoretically based young adult mediators (e.g., life milestones, lifestyle, self-efficacy), and the roles of demographic and other factors as effect modifiers, and (4) develop and test an overall quantitative model for the roles of individual and environmental factors in childhood, adolescence, and young adulthood in predicting changes in smoking-related behaviors during young adulthood. This study is expected to yield timely and critically needed information on smoking acquisition, cessation and relapse during young adulthood, and on the influences of individual, social, and environmental factors. The results can be expected to help identify possible timings and strategies for future public health interventions, and thereby contribute to the smoking and cancer mortality reduction goals of the National Cancer Program. [unreadable] [unreadable]